1. Field of the Invention
The invention relates to a control apparatus and control method of a powertrain. More particularly, the invention relates to technology that controls output torque of a powertrain during a shift in a transmission.
2. Description of the Related Art
A transmission is known that automatically establishes speeds according to the combination of friction apply elements that are to be applied from among a plurality of friction apply elements. In such a transmission, a shift is performed by applying a friction apply element that is in a released state and releasing a different friction apply element that is in an applied state.
During an upshift in the transmission, after a torque phase in which only the torque load of the friction apply elements changes while the input shaft rotation speed remains the same, an inertia phase starts in which the input shaft rotation speed decreases. If the torque input to the transmission during the shift is constant, it is known that the output torque of the transmission will decrease during the torque phase and increase during the inertia phase. If the torque fluctuation is large, shock may be generated as a result. Therefore, in order to reduce shock during a shift (i.e., shift shock), technology has been proposed which increases the input torque of the transmission during the torque phase and decreases that input torque during the inertia phase.
Japanese Patent Application Publication No. 5-263911 (JP-A-5-263911) describes a control apparatus for an automatic transmission that reduces shift shock in a vehicle with an automatic transmission as much as possible by finely electronically controlling the engine output. This control apparatus gradually retards the ignition timing from the timing at which the shift start command was output, and then advances the ignition timing to the regular ignition timing at an appropriate time constant once the torque phase starts. When the inertia phase starts, the ignition timing is retarded to an appropriate predetermined value, and when the inertia phase ends, the ignition timing is advanced to the regular ignition timing.
According to the control apparatus described in JP-A-5-263911, after the shift command is output, the engine torque is slowly reduced so that the output torque at the start of the torque phase is reduced. At the torque phase, the engine torque can be increased. Once the inertial phase starts, the engine torque is gradually reduced so that the amount of increase in the output torque from inertia can be reduced. Accordingly, a drop in torque during the torque phase can be kept to a minimum. Also, a sudden increase in torque during the inertia phase can also be suppressed. As a result, shift shock can be reduced.
Incidentally, in order to achieve good shift characteristics, the hydraulic pressure to be supplied to the friction apply elements during shifting is not constant. For example, when the friction apply elements become worn, more pressure is needed to obtain the same apply force. Therefore, in a transmission the hydraulic pressure supplied to the friction apply elements is corrected based on such factors as the rate of change in the input shaft rotation speed during shifting. For example, if the rate of decrease in the input shaft rotation speed is less than a preset rate of decrease, the friction apply element is considered to be worn so the hydraulic pressure supplied to that friction apply element when it is to be applied for a shift is increased.
Increased hydraulic pressure will cause the torque phase to start earlier during an upshift. Therefore, even if the engine torque is increased during the torque phase, as it is with the control apparatus described in JP-A-5-263911, the lag between the timing at which the torque phase starts and the timing at which the engine torque increases may increase. In this case, even if the engine torque is increased, the range of the decrease in the output torque may increase. As a result, the shock that may be generated during the shift may increase. In JP-A-5-263911, however, there is no mention whatsoever of this kind of problem.